Electrical connector



Aug' 13, 1968 J. s. PRIFOGLE ET AL 3,397,383

ELECTRICAL CONNECTOR Filed April 11, 196e United States Patent O 3,397,383 ELECTRICAL CONNECTOR John S. Prifogle, Williamsburg, aud Richard C. Vail, Richmond, Ind., assignors to Belden Corporation, a corporation of Illinois Filed Apr. 11, 1966, Ser. No. 541,771 4 Claims. (Cl. 339-252) ABSTRACT F THE DISCLOSURE A spring blade is provided which extends from and is supported in a plug body. The spring blade comprises a flat metal strip which is folded upon itself to provide an outer contact portion, a shank portion and an intermediate contact portion connecting the outer contact portion with the shank portion, the outer contact portion includes tirst coextensive substantially parallel adjacent sections of the strip, the intermediate contact portion includes second coextensive sections of the strip. These second coextensive sections are bowed outwardly from each other to provide compressional resiliency for the intermediate contact portion. The spring blade also includes a stilfener strip extending between the second coextensive sections and between the first coextensive sections for imparting lateral and torsional rigidity to the spring blade. The spring blade further comprises means supported either by the stiifener portion between the second coextensive sections or by the second coextensive sections for limiting inward movement of the second coextensive sections so that permanent deformation does not occur when the second coextensi-ve sections are urged toward each other.

This invention relates to electrical plug connectors and the like and, more particularly, to an improved spring blade terminal or prong for such connectors.

The usual electrical plug connector of the subject type comprises a body of insulating material, having passages therein for an electrical conductor or conductors, and having two or more blade terminals or prongs to which the electrical conductors are attached. The terminals are supported by, and project outwardly from, the insulating body and are adapted to engage the contacts of a receptacle or other power outlet when inserted therein. Plug connectors of this type are often used for connecting appliance cords to wall receptacles and similar electrical power outlets. For safety reasons, the plug connector body is often made of a soft, unbreakable material such as a resilient plastic compound, although many plug connectors are comprised of separable portions of hard or breakable material.

In order to provide good electrical contact between the blade terminals of plug connectors and the cooperating contacts of receptacles or other power outlets, electrical plug connectors often utilize compressibly resilient spring blade terminals. The spring blades assure that good electrical contact is made with the contacts of receptacles or other power outlets regardless of wear or loss of resilience in the receptacle or outlet contacts. A satisfactory construction for a spring blade terminal of the type described is disclosed in United States Patent No. 2,439,767, issued Apr. 13, 1948, and assigned to the assignee of the present invention. Such a spring blade terminal includes a metal strip folded back upon itself to form an outer contact portion, a shank portion, and an intermediate portion connecting the outer contact portion to the shank portion. The shank portion is adapted to be embedded in the plug body and the contact portion is adapted to engage the contact in the receptacle. The intermediate portion is comprised of two outwardly bowed coextensive sections, which are resiliently compressible and are ice adapted to grip the inner surfaces of the slotted portion of the receptacle and thereby assure that the outer contact lportion is urged against the receptacle contact. This reduces shifting of the spring blade in the receptacle contact which causes arcing and burning and also reduces the tendency of the spring blade to fall out of the receptacle when the contact becomes worn or when the blade becomes displaced by the weight of the cord.

Certain problems are someti-mes encountered in connection with spring blades of the type described in the aforesaid patent. One such problem, which occurs frequently when the plug connector is subject to rough treatment in use, is that excessive lateral or torsional force applied to the spring blades may cause the blades to permanently bend or twist. When this occurs, the insertion of the spring blade terminals of the plug connector into a receptacle may become difficult or impossible. Another problem which occurs in connection with spring blades of the type described is that the outwardly bowed strip sections of the spring blades may be subject -to excessive compressive forces, due to rough use or a faulty receptacle, such as to deform such sections beyond the elastic limit of the material of which they are comprised. This permanent deformity may seriously curtail or even destroy the advantages accruing from the resilient nature of the spring blade.

Although certain types of reinforce-ment may prevent permanent bending, twisting or deforming of the spring blade, such reinforcing may be difficult to accomplish without severely limiting the usefulness of the spring blade. For example, the reinforcing device or structure may interfere with the resilient action of the blade under compression and limit its ability to provide good electrical contact with worn or deformed receptacle contacts. Moreover, the additional device or structure providing reinforcement may add such cost to the spring blade, both with respect to additional parts and material required and with respect to additional operations necessary for assembly, as to render the spring blade too expensive for competitive marketing.

It is therefore an object of this invention to provide an improved spring blade 'for electrical plug connectors and the like.

Another object of the invention is to provide a reinforced spring blade which retains full resiliency and which is economical in cost.

Still another object of the invention is to provide a spring blade which is relatively difficult to bend or twist.

A futher object of the invention is to provide a spring lblade in which it is relatively difficult to deform the bowed sections thereof beyond their elaastic limit.

Other objects and the various advantages of the invention will become apparent to those skilled in the art Ifrom the following description taken in connection with the accompanying drawings wherein:

FIGURE l i-s an elevational full section view of an electrical plug connector incorporating certain features of the invention;

FIGURE 2 is a perspective view, with part broken away, of the spring blade used in the plug connector of FIGURE l;

FIGURE 3 is a fragmentary perspective view of another embodiment of the spring blade;

FIGURE 4 is a perspective View, with part broken away, of a spring blade constructed in accordance with another embodiment of the invention;

FIGURE 5 is a perspective view of a spring bla-de conructed in accordance with still :another embodiment of the invention; and

FIGURE 6 is a fragmentary view of a still further embodiment of the spring blade.

- The preferred embodiment of the spring blade is shown in FIGURE 1. Briefly, the spring blade which is indicated by the reference numeral 6, extends from and is supported in a plug body 8. The spring blade 6 comp-rises a flat metal strip 10 which is folded upon itself to provide an outer contact portion 12, a shank portion 14, and an intermediate contact portion 16 connecting the outer contact portion with the shank portion. The shank portion 14 includes means 18 for supporting the spring blade 6 in the plug body 8. The shank portion 14 also includes means 20 for making electrical connection to a conductor 22 in the plug body v8. The outer contact portion 12 in cludes rst coextensive substantially parallel 'adjacent sections of the strip 10. The intermediate contact portion includes second coextensive sections of the strip 10. These latter sections 16 are bowed outwardly from each other to provide compressional resiliency for the intermediate contact portion. The spring blade 6 also includes a stiffener portion 24 comprising a single section of the metal strip 10 folded upon the shank portion 14 and extending between the second coextensive sections and between the rst coextensive sections 12 for imparting rigidity to the spring blade. The spring blade 6 further comprises means 26 supported by the stilfener portion 24 between the second coextensive sections for limiting inward movement of the second coextensive sections so that permanent deformation does not occur when the second coextensive sections are urged toward each other.

Referring now more particularly to the drawing, FIG- URE l shows an electrical plug connector of a type in which the invention may be used. The connector is comprised of the plug body 8 of insulating material and a lpair of the spring blades -6, which are sometimes referred to as prongs, extending from one end of the body 8. The illustrated plug body 8 is of a molded construction but it is to be understood that alternative constructions are possible Within the scope of this invention. For example, the body may be comprised of several connected pieces of rigid plastic or similar material.

Referring now also to FIGURE 2, each spring blade `6 is formed from the at metal strip 10 which is of uniform width and of suitable spring material. The strip 10 is folded back upon itself to provide the outer transversely resilient contact portion 12, the intermediate transversely resilient contact portion 16, and the shank or support portion 14. The shank portion 14 constitutes an extension of the Contact portions 12 and 16 and is yadapted to be molded into the plug connector body S.

The outer contact portion 12 comprises coextensive s-ubstantially parallel adjacent sections of the strip It) which are spaced a short distance apart. In certain instances it has been found desirable to provide a slight taper to the two -sections of the outer contact portion 12, the taper being in such direction as to provide the minimum blade thickness at the outer extremity of the blade. The term substantially parallel as used herein is intended to include constructions which may be slightly tapering or which are truly parallel.

In accordance with Underwriters Laboratory requirements, a hole 28 is provided in each of the two sections of the outer contact portion 12. These holes are mutually aligned and provide an interlocking engagement with the stationary contacts of the standard receptacle by engaging projections on the receptacle contact. The rim of each hole 28 is indented to form an annular inner projection or indentation 30. These projections 30 limit but do not prevent movement of the two sections 12 toward each other.

The illustrated intermediate contact portion 16 has a length approximately equal to the length of the outer contact portion 12 and comprises symmetrical outwardly bowed coextensive sections of the strip 10. The bowing of the coextensive sections of intermediate contact portion 16 makes the latter portion substantially wider than the outer contact portion 12. The resiliency of the material in the metal strip 10 enables the coextensive sections of intermediate contact portion 16 to be moved toward each other when the spring blade is inserted in a receptacle. This resilience insures that electrical Contact i-s maintained despite the condition of the contacts in the receptacle, and also provides a physical holding force for the plug connector in the receptacle.

The shank portion 14 of the spring blade includes the means 18 for supporting t-he spring blade in the body 8 and the means 20 for making electrical contact with the conductor 22. The supporting means 18 is in the form of a ledge which extends normally from the rest of the shank portion 14 and which is formed by a double fold in one of the two sections of the metal strip 10 which comprise the shank portion 14. The ledge 18 provides stabilization and anchoring for the spring blade so that the blade is securely held in position within the body 8. The other of the two sections 14 extends beyond the ledge 18 and is provided with the contact making means 20. The illustrated contact making means 20' includes a pair of integral tabs or ears 32 and 34 which may be deformed to hold an end of the conductor 22 in electrical contact with the spring blade. The ledge 18 helps to position the conductor 22 by providing a stop -for the end of the conductor when it is inserted between the tabs 32 and 34. If desired, the conductor 22 may be soldered to the spring blade at the tabs 32 and 34. The tabs 32 and 34 mechanically hold the conductor in proper alignment during the handling and assembling of the spring blade 6 into the body 8 and also serve as additional anchoring for the blade in the body 8. It should be pointed out that the particular described construction for the shank portion 14 is merely a preferred form, and that the shank portion may take various other suitable forms. For exlample, a conventional insulation clam-p (not shown) may be integrally connected to the lower end of the tabs for clamping the insulation of the conductor in place.

Under certain conditions in the eld particularly rough treatment, the spring Iblades 6 may be subjected to stresses of a magnitude which may cause twisting, bending or deforming of the 1blades. When this occurs, the spring blades 6 may be diicult or impossible to insert properly in a receptacle. Furthermore, the bending, twisting or deforming may result in poor electrical connection between the spring fblades 6 and the contacts in the receptacle. For example, if the spring -blade 6 is subject to excessive transverse or torsional forces, it may bend or twist at the point Where it enters the plug body 8. In addition, excessive compressional force exerted on the intermediate contact portion 16, as a result, for example, of faulty receptacle construction, may Hex the coextensive sections of the intermediate contact portion 16 to such an extent that they become permanenly deformed.

Provision for reinforcement of the spring blade 6 in o'rder to prevent bending, twisting and deformation thereof is complicated `by several factors. Among these is the fact that the spacing and the width of the rigid slot openings in the receptacle may both vary over a relatively large range (i.e., .025 to .030) and still meet Underwriters Laboratory requirements. The bowed intermediate portion 16 should preferably have a considerable amount of resilience in order to grip properly in the wide receptacle slots and yet permit the blades to be inserted in the narrow slots without permanent deformation. The reinforcing should not interfere with this resilient compression of the intermediate contact portion 16. Moreover, the outer contact portion 12 should preferably be movable somewhat sideways so that a pair of blades on a plug can be inserted in a receptacle with the wider spaced slots as well las the receptacle with the narrower spaced slots. Also, it is preferable that the outer contact portion 12 after reinforcing be resiliently compressible to accommodate variations in the width of the opening in the receptacle contact. Furthermore, reinforcing generally means additional material, additional parts, and increased assembly time and operations. In order to maintain the cost of the spring blade at competitive levels, the cost of the reinforcing should fbe minimized.

In the spring blade of FIGURES 1 and 2, reinforcing is provided by means of the stiffener portion 24 comprising a single section of the metal strip which is folded back between the two sections of the shank portion 14. The stiffener portion 24 extends between the two coextensive sections of the intermediate contact portion 16, and terminates between the -two coextensive sections of the outer contact portion 12. Preferably, the spacing between the two coextensive sections 12 is made greater than the thickness of the stiffening portion 24. In this way, the blade 6 can bend, slightly before the stitfening portion 24 contacts one of the interior surfaces of outer contact portion 12. This accommodates variations in spacing between receptacle slots, as Well as variations in contact size, slot opening, etc. However, once the stiffener portion 24 is contacted, it aids in resisting the lateral force. In the event of torsional forces applied to the blade 6, the stiffener portion 24 operates in a similar fashion to engage the outer contact portion 12 and provide reinforcement after the allowable amount of twisting has occurred. Because the stitfener portion 24 is merely an extra length of the metal strip 10 which is folded back on the shank portion, a simple modification may be made in the manufacturing operation for spring blades to incorporate the additional reinforcing. No added parts are necessary and assembly cost is thereby minimized.

In order to prevent compression of intermediate contact portion 16 beyond the stress limit of the strip material of which it is comprised, a iexation limiting means 26 is provided between the two sections of the intermediate contact portion 16. In the embodiment of FIG- URES 1 and 2, the exation limiting means 26 comprises a center rigid projection 36 and a pair of flanking rigid projections 37 and 38 which are formed in the stiifener portion 24 intermediate the ends of the intermediate contact portion 16. As illustrated particularly in FIGURE 2, the flanking projections 37 and 38 project in a direction opposite that of the center projection 36. The projections 36, 37 and 38 may be formed by lancing at approximately two points and displacing the two outer portions in one direction and the center portion in the opposite direction. The anking projections 37 and 38 are separated from the center projection 36 a distance suicient to limit inward movement of the coextensive sections of intermediate contact portion 16 to a magnitude which prevents permanent deformation of the same. The distance which the anking projections 37 and 38 and the center projection 36 are spaced from the coextensive sections of intermediate contact portion 16 determines the amount of inward movement allowed and is made suiicient to allow insertion of the blade in the narrower receptacle slot while still assuring proper gripping thereof. The amount of movement allowed is made less than that required to exceed the stress limit of the coextensive sections and cause permanent deformation.

FIGURE 3 shows a second embodiment of the flexation limiting means. In this embodiment, wherein similar parts are identified with the same reference numerals with the subscript a, the flexation limiting means 26a includes a pair of oppositely directed projections 39 and 40 which are formed by lancing the stiffener portion 24a in the center and displacing each half in opposite directions.

Referring now to FIGURE 4, another embodiment of the spring blade is shown. This embodiment is generally similar to the embodiment shown in FIGURES 1 and 2 and parts similar to those shown in FIGURES l and 2 are indicated with the same reference numerals with the subscript b. The primary difference between the embodiment of FIGURE 4 and the embodiment of FIGURES 1 and 2 lies in the location of the flexation limiting means 2617. As illustrated in FIGURE 4, the exation limiting means includes a pair of projections 41 and 42 extending inwardly from the coextensive sections of intermediate contact portion 16b. The illustrated projections 41 and 42 are comprised of tabs which are lanced in the metal strip at the coextensive sections of intermediate contact portion 161g. 'Ihe size of the projections 41 and 42 is such that the projections are effectively rigid and the distance which the projections extend inwardly is selected such that they will engage stiffener portion 24b upon a predetermined inward flexing of intermediate contact por-tion 16b.

Under some circumstances, stilfening reinforcement for the purposes of resisting excessive bending and twisting forces may be unnecessary. Under such circumstances, a. configuration as shown in FIGURE 5 may be utilized. The spring blade shown in FIGURE 5 is constructed in similar manner to the embodiment shown in FIGURE 4 and similar parts are indicated with the same reference numeral and the subscript c. In this embodiment, the ledge 18e` is formed of a single thickness of the metal strip 10c and the outermost edge of the ledge 18e is the terminating end of the metal strip. The two sections of the shank portion 14c are immediately adjacent each other and are not separated by a stiffener portion as was the case in the previous two embodiments.

FIGURE 6, wherein parts similar to FIGURE 4 are indicated with the same reference numeral and the subscript d, shows still another construction of the flexation limiting means 26d. In this embodiment, the flexation limiting means 26d is comprised of a pair of inward directed indentations 44 and 46 respectively formed in the coextensive sections of the intermediate contact portion 16d.

It may therefore be seen that the invention provides an improved spring blade for electrical plug connectors which is reinforced against twisting, bend, and deformation. The blade retains all the advantages of previously known spring blade constructions insofar as resilience and adaptability are concerned, and is of economical construction.

Various changes and modifications may be made in the spring blade without deviating from the spirit or scope of the invention. Various -features of the invention are set forth in the accompanying claims.

What is claimed is:

1. A spring blade for electrical plug connectors, comprising a at metal strip which is folded upon itself to provide an outer contact portion, a shank portion, and an intermediate contact portion connecting said outer contact portion with said shank portion, `said shank portion including means for supporting said spring blade in a body of the plug connector and means for making electrical connection to a conductor in the body of the plug connector, said outer contact portion including irst coextensive substantially parallel adjacent sections of said strip, said intermediate contact portion including second coextensive sections of said strip which are bowed outwardly from each other to provide compressional resiliency for said intermediate contact portion, a stiiener strip extending from said shank portion between said second coextensive sections and said first coextensive sections for imparting further lateral and torsional rigidity to said spring blade and exation limiting means supported between said second coextensive sections and said stiffener strip so that said exation limiting means coacts with said stiffener strip and said second coextensive sections to limit the inward flexation of the second coextensive sections to magnitude less than that which causes permanent deformation of said second coextensive sections.

2. A spring blade in accordance with claim 1 wherein said flexation limiting means comprises a pair of projections, one on each of said second coextensive sections and extending therefrom toward the other of said projections.

3. A spring blade in accordance with claim 1 wherein said exation limiting means is supported by said stiffener strip and extends rigidly from opposite sides thereof.

4. A spring blade in accordance with claim 3 wherein said exation limiting means includes a center projection and a pair of anking projections which project in a direction opposite that of the center projection.

References Cited UNITED STATES PATENTS McFadden 339-196 X Gardner 339-195 Olson 339-252 Anderson 339-252 Mangold 339-196 Gilbert 339-62 X Sapper et al 339-62 X MARVIN A. CHAMPION, Primary Examiner.

10 P. TEITELBAUM, Assistant Examiner. 

